9 June 2012

Don't wee with fright when candiru are about!

"You mustn't wee in the Amazon River, whatever you do." How many of you have heard this phrase before, or at least something along these lines? Many people of course have and the first thing that this makes many think of is the infamous fish that lurks in the waters of the Amazon River; a fish that is just waiting to swim up the most private and delicate parts of unsuspecting swimmers!

This fish can't be real, can it? I mean, the whole idea sounds like something you would see on a dodgy SciFi 'B movie' - the sort of film where after it's finished, you know that you've just wasted an hour and half of your life that you're never going to see again... Many people are sceptical of this whole idea, yet despite how preposterous it sounds the popular urban myth has been around for centuries - with the earliest anecdotal records dating back to the early 1900s! So does it have some truth?

The candiru, Vandellia cirrhosa, are small fish that are native to the Amazon River and are infamous for the urban legends which claim that they invade the urethra of men and women that wee in the river!

First, let us look at the culprit - the candiru, which is also called the 'vampire' or 'toothpick' fish. The candiru is a species of freshwater catfish that parasitises the gills of the larger fish that live in the Amazon Basin, where it lodges itself between two of its victim's gills and gorges on its blood. It accomplishes this using short, backwards-facing barbs that surround its head and hold the candiru firmly in place and once it is well and truly lodged in, the candiru remains until it has had its fill of blood. Once full, its barbs are retracted and the bloated fish swims off to digest its stolen meal in relative peace. Judging by this method of feeding then, the fish certainly sounds capable of invading a human urethra; well it would do, except for one major problem. The width of the head of the candiru can easily grow to be over 10cm, which means that the force required to push itself into a human urethra (especially for a man) would be enormous - probably much greater than the fish can muster. Furthermore, the fish lacks any specialised 'entry' organs to make this easier, instead seeming to simply rely on brute force. This heavy-handed method of entry is definitely feasible for their usual victims since fish gills are wiper apart so are much easier to invade, but does it really allow them to enter human orifices?

Many people firmly believe that the fish can, despite this criticism and there are in fact many anecdotal reports that say that is the case. For example, many of the local tribes that live in the haunts of the candiru wear specialised garments to protect their genitals when bathing in the Amazon and there is a documented account from the biologist George Boulenger that details a group of men from Brazilian tribes that had had their penises amputated, supposedly due to candiru parastitism. Note however, that there was a language barrier in this case and none of the tribesmen spoke English; something that led to much confusion when Boulenger was researching their claims! These weak claims make it difficult to speculate whether or not the candiru can swim up a man's penis, especially since many other Amazonian tribes wear similar genital-protective garments to protect against piranha bites and not candiru attacks...

However, there are much more numerous and reliable accounts of the candiru invading the female vagina (although this fact has been breezed over in the popular myths) and that they can do this is widely accepted in the scientific and medial community, as numerous biologists and reputable physicians have given detailed accounts of removing the fish from the vaginal canals of patients. In fact, this is actually biologically plausible since candiru hunt by following the streams of urine that are released from the gills of fish as they swim and a stream of urine from a human isn't all that different; meaning that it could possibly attract the candiru and whereas the urethra in the penis in very narrow so even if the fish was attracted it is unlikely that they could swim up into it, the vagina is obviously much wider - possibly even wide enough for the fish to force its way into! 

This X-ray shows a candiru fish that has lodged itself in the vagina of a poor women, who is undoubtedly in a lot of pain. Fortunately, the fish can be removed with relatively little damage to the surrounding tissue although the procedure is undoubtedly uncomfortable to say the least!

Thus, it is likely that the myths may actually be real! Although it is doubtful whether they can swim up into a man's penis. Women on-the-other-hand, may be much more at risk from invasion by the candiru so should take much greater care not to wee in the murky waters of the Amazon River! Regardless of your gender however and even if you fiercely disbelieve the myths, urination in the river should still be avoided at all costs. Many of the species of fish that live there respond aggressively to sudden increases in the concentration of urine (although scientists aren't really sure why) and you could easily instigate an attack on yourself - an attack made worse as the waters of the Amazon are so cloudy you can't see very far below its surface to see the attacker!

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